Bonded semiconductor structures having bonding contacts made of indiffusible conductive materials and methods for forming the same

ABSTRACT

Embodiments of bonded semiconductor structures and fabrication methods thereof are disclosed. In an example, a semiconductor device includes a first semiconductor structure, a second semiconductor structure, and a bonding interface between the first semiconductor structure and the second semiconductor structure. The first semiconductor structure includes a substrate, a first device layer disposed on the substrate, and a first bonding layer disposed above the first device layer and including a first bonding contact. The second semiconductor structure includes a second device layer and a second bonding layer disposed below the second device layer and including a second bonding contact. The first bonding contact is in contact with the second bonding contact at the bonding interface. At least one of the first bonding contact or the second bonding contact is made of an indiffusible conductive material.

CROSS REFERENCE TO RELATED APPLICATION

This application is continuation of International Application No.PCT/CN2019/074803, filed on Feb. 11, 2019, entitled “BONDEDSEMICONDUCTOR STRUCTURES HAVING BONDING CONTACTS MADE OF INDIFFUSIBLECONDUCTIVE MATERIALS AND METHODS FOR FORMING THE SAME,” which is herebyincorporated by reference in its entirety.

BACKGROUND

Embodiments of the present disclosure relate to bonded semiconductorstructures and fabrication methods thereof.

Planar semiconductor devices, such as memory cells, are scaled tosmaller sizes by improving process technology, circuit design,programming algorithm, and fabrication process. However, as featuresizes of the semiconductor devices approach a lower limit, planarprocess and fabrication techniques become challenging and costly. Athree-dimensional (3D) device architecture can address the densitylimitation in some planar semiconductor devices, for example, Flashmemory devices.

A 3D semiconductor device can be formed by stacking semiconductor wafersor dies and interconnecting them vertically using, for instance,through-silicon vias (TSVs) or copper-to-copper (Cu—Cu) connections, sothat the resulting structure acts as a single device to achieveperformance improvements at reduced power and smaller footprint thanconventional planar processes. Among the various techniques for stackingsemiconductor substrates, hybrid bonding is recognized as one of thepromising techniques because of its capability of forming high-densityinterconnects.

SUMMARY

Embodiments of semiconductor devices, bonded structures, and fabricationmethods thereof are disclosed herein.

In one example, a semiconductor device includes a first semiconductorstructure, a second semiconductor structure, and a bonding interfacebetween the first semiconductor structure and the second semiconductorstructure. The first semiconductor structure includes a substrate, afirst device layer disposed on the substrate, and a first bonding layerdisposed above the first device layer and including a first bondingcontact. The second semiconductor structure includes a second devicelayer and a second bonding layer disposed below the second device layerand including a second bonding contact. The first bonding contact is incontact with the second bonding contact at the bonding interface. Atleast one of the first bonding contact or the second bonding contact ismade of an indiffusible conductive material.

In another example, a bonded structure includes a first bonding layerincluding a first bonding contact and a first dielectric, a secondbonding layer including a second bonding contact and a seconddielectric, and a bonding interface between the first bonding layer andthe second bonding layer. The first bonding contact is in contact withthe second bonding contact at the bonding interface, and the firstdielectric is in contact with the second dielectric at the bondinginterface. Each of the first bonding contact and the second bondingcontact is made of a same indiffusible conductive material other thancopper (Cu).

In still another example, a method for forming a semiconductor device isdisclosed. A first device layer is formed above a first substrate. Afirst bonding layer including a first bonding contact is formed abovethe first device layer. The first bonding contact is made of a firstindiffusible conductive material. A second device layer is formed abovea second substrate. A second bonding layer including a second bondingcontact is formed above the second device layer. The first substrate andthe second substrate are bonded in a face-to-face manner, such that thefirst bonding contact is in contact with the second bonding contact at abonding interface.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates a cross-section of an exemplary bonded semiconductordevice including bonding contacts made of an indiffusible conductivematerial, according to some embodiments of the present disclosure.

FIG. 2 illustrates a cross-section of an exemplary bonded structureincluding bonding contacts made of an indiffusible conductive material,according to some embodiments of the present disclosure.

FIGS. 3A-3C illustrate an exemplary fabrication process for forming afirst semiconductor structure including bonding contacts made of anindiffusible conductive material, according to some embodiments of thepresent disclosure.

FIGS. 4A-4C illustrate an exemplary fabrication process for forming asecond semiconductor structure including bonding contacts made of anindiffusible conductive material, according to some embodiments of thepresent disclosure.

FIGS. 5A-5B illustrate an exemplary fabrication process for bonding thefirst semiconductor structure and the second semiconductor structure,according to some embodiments of the present disclosure.

FIG. 6 is a flowchart of an exemplary method for forming a semiconductordevice including bonding contacts made of an indiffusible conductivematerial, according to some embodiments of the present disclosure.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which interconnect lines and/or via contacts are formed) and one ormore dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND memory strings) ona laterally-oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, theterm “vertical/vertically” means nominally perpendicular to the lateralsurface of a substrate.

In the high density, low feature size (e.g., 100 nm) hybrid bondingprocess, metals of bonding contacts in the two semiconductor structuresused as the conductor layers include copper. Copper migration, however,can happen during the hybrid bonding process due to thermal expansion orduring the usage life time and thus, can lead to void formation in thebonding contacts after bonding. Moreover, diffusion of copper at thebonding interface is another problem for hybrid bonding, which can causeleakage and shorten electromigration (EM) life of the bonded structure.

Various embodiments in accordance with the present disclosure providebonding contacts made of an indiffusible conductive material forimproving a hybrid bonding interface. By replacing copper withindiffusible conductive materials, copper diffusion through the bondinginterface can be avoided, thereby reducing leakage and increasing EMlife of the bonded structure. Fabrication processes for forming bondinglayers including the bonding contacts made of indiffusible conductivematerials can be adjusted from the traditional copper bonding contactprocesses based on the specific indiffusible conductive material used bythe bonding contacts.

FIG. 1 illustrates a cross-section of an exemplary bonded semiconductordevice 100 including bonding contacts made of an indiffusible conductivematerial, according to some embodiments of the present disclosure. Forease of description, bonded semiconductor device 100 will be describedas a non-monolithic 3D memory device. However, it is understood thatbonded semiconductor device 100 is not limited to a 3D memory device andcan include any suitable bonded semiconductor devices that can usebonding contacts made of an indiffusible conductive material to avoidcopper diffusion at the bonding interface as described below in detail.It is understood that bonded semiconductor devices that include bondingcontacts made of an indiffusible conductive material as disclosed hereinare not limited to the example shown in FIG. 1 and can include any othersuitable semiconductor devices, such as logic devices, volatile memorydevices (e.g., dynamic random-access memory (DRAM) and staticrandom-access memory (SRAM)), and non-volatile memory devices (e.g.,NAND or NOR Flash memory), in a 2D, 2.5D, or 3D architecture.

Bonded semiconductor device 100 represents an example of anon-monolithic 3D memory device. The term “non-monolithic” means thatthe components of bonded semiconductor device 100 (e.g., peripheraldevices and memory array devices) can be formed separately on differentsubstrates and then bonded to form a bonded semiconductor device. Bondedsemiconductor device 100 can include a substrate 102, which can includesilicon (e.g., single crystalline silicon), silicon germanium (SiGe),gallium arsenide (GaAs), germanium (Ge), silicon on insulator (SOI), orany other suitable materials.

It is noted that x and y axes are included in FIG. 1 to furtherillustrate the spatial relationship of the components in bondedsemiconductor device 100 having substrate 102. Substrate 102 includestwo lateral surfaces (e.g., a top surface and a bottom surface)extending laterally in the x-direction (i.e., the lateral direction). Asused herein, whether one component (e.g., a layer or a device) is “on,”“above,” or “below” another component (e.g., a layer or a device) of asemiconductor device (e.g., bonded semiconductor device 100) isdetermined relative to the substrate of the semiconductor device (e.g.,substrate 102) in the y-direction (i.e., the vertical direction) whenthe substrate is positioned in the lowest plane of the semiconductordevice in the y-direction. The same notion for describing spatialrelationship is applied throughout the present disclosure.

Bonded semiconductor device 100 can include two semiconductorstructures, i.e., a memory array device chip 160 and a peripheral devicechip 162 bonded in a face-to-face manner at a bonding interface 158. Insome embodiments, bonding interface 158 is disposed between memory arraydevice chip 160 and peripheral device chip 162 as a result of hybridbonding (also known as “metal/dielectric hybrid bonding”), which is adirect bonding technology (e.g., forming bonding between surfaceswithout using intermediate layers, such as solder or adhesives) and canobtain metal-metal bonding and dielectric-dielectric bondingsimultaneously. In some embodiments, bonding interface 158 is the placeat which memory array device chip 160 and peripheral device chip 162 aremet and bonded. In practice, bonding interface 158 can be a layer with acertain thickness that includes the bottom surface of memory arraydevice chip 160 and the top surface of peripheral device chip 162. It isunderstood that although memory array device chip 160 is disposed aboveperipheral device chip 162 in FIG. 1, their relative positions can bereversed in some embodiments. For example, memory array device chip 160can be disposed below peripheral device chip 162 in another bondedsemiconductor device.

Peripheral device chip 162 can include a peripheral device layer 103 onsubstrate 102. Peripheral device layer 103 can include a plurality oftransistors 104 formed on substrate 102. Transistors 104 can be formed“on” substrate 102, where the entirety or part of each transistor 104 isformed in substrate 102 (e.g., below the top surface of substrate 102)and/or directly on substrate 102. Isolation regions (e.g., shallowtrench isolations (STIs), not shown) and doped regions (e.g., sourceregions and drain regions of transistors 104, not shown) can be formedin substrate 102 as well.

In some embodiments, peripheral device layer 103 can include anysuitable digital, analog, and/or mixed-signal peripheral circuits usedfor facilitating the operation of bonded semiconductor device 100. Forexample, peripheral device layer 103 can include one or more of a pagebuffer, a decoder (e.g., a row decoder and a column decoder), a senseamplifier, a driver, a charge pump, a current or voltage reference, orany active or passive components of the circuits (e.g., transistors,diodes, resistors, or capacitors). In some embodiments, peripheraldevice layer 103 is formed on substrate 102 using complementarymetal-oxide-semiconductor (CMOS) technology (in this case, peripheraldevice chip 162 is also known as a “CMOS chip”).

Peripheral device chip 162 can include an interconnect layer 106(referred to herein as a “peripheral interconnect layer”) aboveperipheral device layer 103 to transfer electrical signals to and fromperipheral device layer 103. Peripheral interconnect layer 106 caninclude a plurality of interconnects 108 (also referred to herein as“contacts”), including lateral interconnect lines and verticalinterconnect access (via) contacts. As used herein, the term“interconnects” can broadly include any suitable types of interconnects,such as middle-end-of-line (MEOL) interconnects and back-end-of-line(BEOL) interconnects. Peripheral interconnect layer 106 can furtherinclude one or more interlayer dielectric (ILD) layers (also known as“intermetal dielectric (IMD) layers”) in which interconnects 108 canform. That is, peripheral interconnect layer 106 can includeinterconnect lines and via contacts in multiple ILD layers.Interconnects 108 in peripheral interconnect layer 106 can includeconductive materials including, but not limited to, copper (Cu),aluminum (Al), tungsten (W), cobalt (Co), silicides, or any combinationthereof. In one example, interconnects 108 are made of Cu. In anotherexample, interconnects 108 are made of Al. The ILD layers in peripheralinterconnect layer 106 can include dielectric materials including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride, lowdielectric constant (low-k) dielectrics, or any combination thereof.

As shown in FIG. 1, peripheral device chip 162 can further include abonding layer 111 at bonding interface 158 and above peripheralinterconnect layer 106 and peripheral device layer 103. Bonding layer111 can include a plurality of bonding contacts 112 and a dielectric 113electrically isolating bonding contacts 112. Bonding contacts 112 can bemade of an indiffusible conductive material. The remaining area ofbonding layer 111 can be formed with dielectric 113 including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof. In one example, dielectric 113is made of silicon oxide. Bonding contacts 112 and dielectric 113 inbonding layer 111 can be used for hybrid bonding as described below indetail. In some embodiments, the step height between dielectric 113 andbonding contacts 112 is between about −20 nm and about 20 nm, such asbetween −20 nm and 20 nm (e.g., −20 nm, −15 nm, −10 nm, −5 nm, 0 nm, 5nm, 10 nm, 15 nm, 20 nm, any range bounded by the lower end by any ofthese values, or in any range defined by any two of these values). Thatis, the top surface of dielectric 113 may be above the top surface ofbonding contacts 112, or vice versa, but not greater than 20 nm.

To avoid Cu diffusion at bonding interface 158 as described above,bonding contacts 112 can be made of an indiffusible conductive materialthat is not Cu. In some embodiments, the indiffusible conductivematerial is a metal selected from the group consisting of cobalt (Co),tantalum (Ta), tungsten (W), titanium (Ti), and nickel (Ni). Comparedwith Cu, the diffusion of Co, Ta, W, Ti, or Ni does not occur at bondinginterface 158 during thermal process or during usage life time. In someembodiments, the indiffusible conductive material is a metal nitrideselected from the group consisting of cobalt nitride (CoN), tantalumnitride (TaN), tungsten nitride (WN), titanium nitride (TiN), and nickelnitride (NiN). That is, the indiffusible conductive material can be thenitrides of the five metals described above that do not diffuse atbonding interface 158 during thermal process or during usage life time.In some embodiments, the indiffusible conductive material is a metalsilicide selected from the group consisting of cobalt silicide (CoSi),tantalum silicide (TaSi), tungsten silicide (WSi), titanium silicide(TiSi), and nickel silicide (NiSi). That is, the indiffusible conductivematerial can be the cobalt silicides of the five metals described abovethat do not diffuse at bonding interface 158 during thermal process orduring usage life time. Accordingly, the indiffusible conductivematerial of bonding contacts 112 can be selected from the groupconsisting of Co, Ta, W, Ti, Ni, CoN, TaN, WN, TiN, NiN, CoSi, TaSi,WSi, TiSi, and NiSi. In some embodiments, bonding contacts 112 are madeof more than one indiffusible conductive material described above. Inaddition to having the indiffusible conductive material(s) as aconductor layer, bonding contacts 112 can also include additionallayer(s), such as an adhesion layer, a barrier layer, and/or a seedlayer. It is understood that in some embodiments, bonding contacts 112only includes the conductor layer made of an indiffusible conductivematerial but does not include any other layers.

In some embodiments, memory array device chip 160 is a NAND Flash memorydevice in which memory cells are provided in the form of an array ofNAND memory strings 114 each extending vertically through memory arraydevice layer 120 and above peripheral device layer 103. Memory arraydevice layer 120 can include NAND memory strings 114 that extendvertically through a plurality of pairs each including a conductor layer116 and a dielectric layer 118 (referred to herein as“conductor/dielectric layer pairs”). The stacked conductor/dielectriclayer pairs are also referred to herein as a “memory stack.” Conductorlayers 116 and dielectric layers 118 in the memory can stack alternatelyin the vertical direction.

As shown in FIG. 1, each NAND memory string 114 can include asemiconductor channel 124 and a dielectric layer (also known as a“memory film”). In some embodiments, semiconductor channel 124 includessilicon, such as amorphous silicon, polysilicon, or single crystallinesilicon. In some embodiments, the memory film is a composite layerincluding a tunneling layer 126, a storage layer 128 (also known as a“charge trap/storage layer”), and a blocking layer (not shown). EachNAND memory string 114 can have a cylinder shape (e.g., a pillar shape).Semiconductor channel 124, tunneling layer 126, storage layer 128, andthe blocking layer are arranged radially from the center toward theouter surface of the pillar in this order, according to someembodiments. Tunneling layer 126 can include silicon oxide, siliconoxynitride, or any combination thereof. Storage layer 128 can includesilicon nitride, silicon oxynitride, silicon, or any combinationthereof. The blocking layer can include silicon oxide, siliconoxynitride, high dielectric constant (high-k) dielectrics, or anycombination thereof.

In some embodiments, NAND memory strings 114 further include a pluralityof control gates (each being part of a word line). Each conductor layer116 in the memory stack can act as a control gate for memory cell ofeach NAND memory string 114. Each NAND memory string 114 can include asource select gate at its upper end and a drain select gate at its lowerend. As used herein, the “upper end” of a component (e.g., NAND memorystring 114) is the end farther away from substrate 102 in they-direction, and the “lower end” of the component (e.g., NAND memorystring 114) is the end closer to substrate 102 in the y-direction.

In some embodiments, memory array device chip 160 further includes asemiconductor layer 130 disposed above and in contact with NAND memorystrings 114. Memory array device layer 120 can be disposed belowsemiconductor layer 130. In some embodiments, semiconductor layer 130includes a plurality of semiconductor plugs 132 electrically separatedby isolation regions. In some embodiments, each semiconductor plug 132is disposed at the upper end of corresponding NAND memory string 114 andfunctions as the drain of corresponding NAND memory string 114 and thus,can be considered as part of corresponding NAND memory string 114.Semiconductor plug 132 can include a single crystalline silicon.Semiconductor plug 132 can be un-doped, partially doped (in thethickness direction and/or the width direction), or fully doped byp-type or n-type dopants.

In some embodiments, memory array device chip 160 includes localinterconnects that are formed in one or more ILD layers and in contactwith components in memory array device layer 120, such as the word lines(e.g., conductor layers 116) and NAND memory strings 114. The localinterconnects can include word line via contacts 136, source line viacontacts 138, and bit line via contacts 140. Each local interconnect caninclude conductive materials including, but not limited to, W, Co, Cu,Al, silicides, or any combination thereof. In one example, localinterconnects are made of Cu. In another example, local interconnectsare made of Al. Word line via contacts 136 can extend vertically throughone or more ILD layers. Each word line via contact 136 can be in contactwith corresponding conductor layer 116 to individually address acorresponding word line of bonded semiconductor device 100. Each sourceline via contact 138 can be in contact with the source of correspondingNAND memory string 114. Bit line via contacts 140 can extend verticallythrough one or more ILD layers. Each bit line via contact 140 canelectrically connect to corresponding semiconductor plug 132 (e.g., thedrain) of NAND memory string 114 to individually address correspondingNAND memory string 114.

Similar to peripheral device chip 162, memory array device chip 160 canalso include interconnect layers for transferring electrical signals toand from NAND memory strings 114. As shown in FIG. 1, memory arraydevice chip 160 can include an interconnect layer 142 (referred toherein as an “array interconnect layer”) below memory array device layer120. Array interconnect layer 142 can include a plurality ofinterconnects 144, including interconnect lines and via contacts in oneor more ILD layers. Interconnects 144 in array interconnect layer 142can include conductive materials including, but not limited to, Cu, Al,W, Co, silicides, or any combination thereof. In one example,interconnects 144 are made of Cu. In another example, interconnects 144are made of Al. The ILD layers in array interconnect layer 142 caninclude dielectric materials including, but not limited to, siliconoxide, silicon nitride, silicon oxynitride, low-k dielectrics, or anycombination thereof.

As shown in FIG. 1, memory array device chip 160 can further include abonding layer 147 at bonding interface 158 and below array interconnectlayer 142 and memory array device layer 120. Bonding layer 147 caninclude a plurality of bonding contacts 148 and a dielectric 149electrically isolating bonding contacts 148. Bonding contacts 148 can bemade of an indiffusible conductive material. The remaining area ofbonding layer 147 can be formed with dielectric 149 including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof. In one example, dielectric 149is made of silicon oxide. Bonding contacts 148 and dielectric 149 inbonding layer 147 can be used for hybrid bonding as described below indetail. In some embodiments, the step height between dielectric 149 andbonding contacts 148 is between about −20 nm and about 20 nm, such asbetween −20 nm and 20 nm (e.g., −20 nm, −15 nm, −10 nm, −5 nm, 0 nm, 5nm, 10 nm, 15 nm, 20 nm, any range bounded by the lower end by any ofthese values, or in any range defined by any two of these values). Thatis, the bottom surface of dielectric 149 may be above the bottom surfaceof bonding contacts 148, or vice versa, but not greater than 20 nm.

To avoid Cu diffusion at bonding interface 158 as described above,bonding contacts 148 can be made of an indiffusible conductive materialthat is not Cu. In some embodiments, the indiffusible conductivematerial is a metal selected from the group consisting of Co, Ta, W, Ti,and Ni. Compared with Cu, the diffusion of Co, Ta, W, Ti, or Ni does notoccur at bonding interface 158 during thermal process or during usagelife time. In some embodiments, the indiffusible conductive material isa metal nitride selected from the group consisting of CoN, TaN, WN, TiN,and NiN. That is, the indiffusible conductive material can be thenitrides of the five metals described above that do not diffuse atbonding interface 158 during thermal process or during usage life time.In some embodiments, the indiffusible conductive material is a metalsilicide selected from the group consisting of CoSi, TaSi, WSi, TiSi,and NiSi. That is, the indiffusible conductive material can be thecobalt silicides of the five metals described above that do not diffuseat bonding interface 158 during thermal process or during usage lifetime. Accordingly, the indiffusible conductive material of bondingcontacts 148 can be selected from the group consisting of Co, Ta, W, Ti,Ni, CoN, TaN, WN, TiN, NiN, CoSi, TaSi, WSi, TiSi, and NiSi. In someembodiments, bonding contacts 148 are made of more than one indiffusibleconductive material described above. In addition to having theindiffusible conductive material(s) as the conductor layer, bondingcontacts 148 can also include additional layer(s), such as adhesionlayer, barrier layer, and/or seed layer. It is understood that in someembodiments, bonding contacts 148 only includes the conductor layer madeof an indiffusible conductive material but does not include any otherlayers.

As described above, bonding contacts 112 in bonding layer 111 ofperipheral device chip 162 can be made of a first indiffusibleconductive material, and bonding contacts 148 in bonding layer 147 ofmemory array device chip 160 can be made of a second indiffusibleconductive material. In some embodiments, the first indiffusibleconductive material is the same as the second indiffusible conductivematerial, meaning that bonding contacts 112 and bonding contacts 148 atopposite sides of bonding interface 158 are made of the sameindiffusible conductive material. In some embodiments, the firstindiffusible conductive material is different from the secondindiffusible conductive material, meaning that bonding contacts 112 andbonding contacts 148 at opposite sides of bonding interface 158 are madeof different indiffusible conductive materials. In some embodiments, thefirst indiffusible conductive material is different from the secondindiffusible conductive material, while both contain the same metal. Inone example, one of the first and second indiffusible conductivematerials is Co, Ta, W, Ti, or Ni, and the other one of the first andsecond indiffusible conductive materials is the corresponding nitride orsilicide of the first indiffusible conductive material. In anotherexample, the first and second indiffusible conductive materials are thenitride and silicide of the one of Co, Ta, W, Ti, or Ni, respectively(e.g., the first indiffusible conductive material is CoN and the secondindiffusible conductive material is CoSi, etc.).

It is understood that in some embodiments, bonding contacts 112 inbonding layer 111 of peripheral device chip 162 or bonding contacts 148in bonding layer 147 of memory array device chip 160 are not made of anindiffusible conductive material described above. In one example,bonding contacts 112 or bonding contacts 148 are made of Cu. In thisexample, Cu diffusion may not be fully avoided but can be reducedcompared with the existing devices in which bonding contacts at bothsides of the bonding interface are made of Cu. In another example,bonding contacts 112 or bonding contacts 148 are made of a conductivematerial other than Cu and the indiffusible conductive materialsdescribed above, such as Al. Nevertheless, at least one of bondingcontacts 112 or bonding contacts 148 are made of an indiffusibleconductive material described above to reduce or even avoid Cu diffusionat bonding interface 158.

As shown in FIG. 1, another interconnect layer 150 (referred to hereinas a “BEOL interconnect layer”) can be disposed above memory arraydevice layer 120 and can include interconnects 152, such as interconnectlines and via contacts in one or more ILD layers. BEOL interconnectlayer 150 can further include contact pads 156 and a redistributionlayer (not shown) at the top portion of bonded semiconductor device 100for wire bonding and/or bonding with an interposer. BEOL interconnectlayer 150 and array interconnect layer 142 can be formed on oppositesides of memory array device layer 120. In some embodiments,interconnects 152 and contact pads 156 in BEOL interconnect layer 150can transfer electrical signals between bonded semiconductor device 100and external circuits.

FIG. 2 illustrates a cross-section of an exemplary bonded structure 200including bonding contacts made of an indiffusible conductive material,according to some embodiments of the present disclosure. FIG. 1illustrates bonded semiconductor device 100 having bonding contacts madeof an indiffusible conductive material, which includes a bondedstructure of memory array device chip 160 and peripheral device chip162. It is understood that the bonding contacts made of an indiffusibleconductive material disclosed herein can be used in any suitable bondedstructures with various arrangements. FIG. 2 illustrates a bondedstructure 200 including a lower bonding layer 202 and an upper bondinglayer 204, according to some embodiments. Lower bonding layer 202 caninclude lower bonding contacts 206 and lower dielectrics 208electrically isolating lower bonding contacts 206. Similarly, upperbonding layer 204 can include upper bonding contacts 210 and upperdielectrics 212 electrically isolating upper bonding contacts 210.Bonded structure 200 can further include a bonding interface 214 formedbetween lower bonding layer 202 and upper bonding layer 204.

As shown in FIG. 2, upper bonding contact 210 is in contact with lowerbonding contact 206, and upper dielectric 212 is in contact with lowerdielectric 208. In some embodiments, at least one of upper bondingcontact 210 or lower bonding contact 206 is made of an indiffusibleconductive material other than Cu, and upper dielectric 212 and lowerdielectric 208 is made of silicon oxide. In some embodiments, each ofupper bonding contact 210 and lower bonding contact 206 is made of thesame indiffusible conductive material other than Cu. The indiffusibleconductive material can be selected from the group consisting of Co, Ta,W, Ti, Ni, CoN, TaN, WN, TiN, NiN, CoSi, TaSi, WSi, TiSi, and NiSi.Upper bonding layer 204 can be bonded with lower bonding layer 202 byhybrid bonding, so that fusion bonding between upper bonding contact 210and lower bonding contact 206 and SiO_(X)-SiO_(X) covalent bondingbetween upper dielectric 212 and lower dielectric 208 can be formedsimultaneously. In some embodiments, a first step height between upperdielectric 212 and upper bonding contact 210 is between about −20 nm andabout 20 nm, and a second step height between lower dielectric 208 andlower bonding contact 206 is between about −20 nm and about 20 nm.

It is understood that bonded structure 200 can include or be combinedwith other structures, such as device layer(s), interconnect layer(s),and substrate(s), to form any suitable semiconductor devices, forexample, logic devices, volatile memory devices (e.g., dynamicrandom-access memory (DRAM) and static random-access memory (SRAM)), andnon-volatile memory devices (e.g., NAND or NOR Flash memory), in a 2D,2.5D, or 3D architecture. For example. as shown in FIG. 2, bondedstructure 200 can further include a lower interconnect layer 216 belowlower bonding layer 202 and a lower device layer 218 below lowerinterconnect layer 216. Bonded structure 200 can further include anupper interconnect layer 220 above upper bonding layer 204 and an upperdevice layer 222 above upper interconnect layer 220. Depending on thespecific type of semiconductor devices having bonded structure 200,upper and lower device layers 222 and 218 can include suitablesemiconductor devices (e.g., diodes, transistors, capacitors, inductors,etc.) and any suitable circuits formed by the semiconductor devices.

FIGS. 3A-3C illustrate an exemplary fabrication process for forming afirst semiconductor structure including bonding contacts made of anindiffusible conductive material, according to some embodiments. FIGS.4A-4C illustrate an exemplary fabrication process for forming a secondsemiconductor structure including bonding contacts made of anindiffusible conductive material, according to some embodiments. FIGS.5A-5B illustrate an exemplary fabrication process for bonding the firstsemiconductor structure and the second semiconductor structure,according to some embodiments. FIG. 6 is a flowchart of a method 600 forforming an exemplary semiconductor device including bonding contactsmade of an indiffusible conductive material, according to someembodiments. Examples of the semiconductor device depicted in FIGS. 3-6include bonded semiconductor device 100 depicted in FIG. 1. FIGS. 3-6will be described together. It is understood that the operations shownin method 600 are not exhaustive and that other operations can beperformed as well before, after, or between any of the illustratedoperations. Further, some of the operations may be performedsimultaneously, or in a different order than shown in FIGS. 3-6.

Referring to FIG. 6, method 600 starts at operation 602, in which afirst device layer is formed above a first substrate. The firstsubstrate can be a silicon substrate. As illustrated in FIG. 3A, adevice layer 304 is formed above a silicon substrate 302. Device layer304 can be a memory array device layer including a plurality of NANDmemory strings (not shown) each extending vertically through a memorystack (not shown) formed above silicon substrate 302.

To form the memory stack, a dielectric stack including an alternatingstack of sacrificial layers (e.g., silicon nitride) and dielectriclayers (e.g., silicon oxide) can be formed on silicon substrate 302 byone or more thin film deposition processes including, but not limitedto, chemical vapor deposition (CVD), physical vapor deposition (PVD),atomic layer deposition (ALD), or any combination thereof. The memorystack then can be formed above silicon substrate 302 by gate replacementprocesses, i.e., replacing the sacrificial layers in the dielectricstack with conductor layers. In some embodiments, fabrication processesto form the NAND memory strings include forming a semiconductor channelthat extends vertically through the dielectric stack, forming acomposite dielectric layer (memory film) between the semiconductorchannel and the dielectric stack, including, but not limited to, atunneling layer, a storage layer, and a blocking layer. Thesemiconductor channel and the memory film can be formed by one or morethin film deposition processes such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

Method 600 proceeds to operation 604, as illustrated in FIG. 6, in whicha first interconnect layer including a first interconnect is formedabove the first device layer. As illustrated in FIG. 3A, an arrayinterconnect layer 306 can be formed above memory array device layer304. Array interconnect layer 306 can include interconnects (not shown),including interconnect lines and via contacts in a plurality of ILDlayers, to make electrical connections with memory array device layer304. In some embodiments, array interconnect layer 306 includes multipleILD layers and interconnects therein formed by multiple processes. Forexample, the interconnects can include conductive materials deposited byone or more thin film deposition processes including, but not limitedto, CVD, PVD, ALD, electrochemical depositions, or any combinationthereof. The ILD layers can include dielectric materials deposited byone or more thin film deposition processes including, but not limitedto, CVD, PVD, ALD, or any combination thereof.

Method 600 proceeds to operation 606, as illustrated in FIG. 6, in whicha first bonding layer including a first bonding contact made of a firstindiffusible material is formed above the first interconnect layer andfirst device layer. A first dielectric can be formed in the firstbonding layer as well. In some embodiments, the first indiffusibleconductive material is not Cu. The first indiffusible conductivematerial can be selected from the group consisting of Co, Ta, W, Ti, Ni,CoN, TaN, WN, TiN, NiN, CoSi, TaSi, WSi, TiSi, and NiSi. The firstbonding layer can be flattened by CMP or etching, such that a first stepheight between the first dielectric and the first bonding contact isbetween about −20 nm and about 20 nm. In some embodiments, the firstinterconnect is made of a conductive material (e.g., Cu or Al) otherthan the first indiffusible conductive material.

As illustrated in FIG. 3B, a dielectric 308 is deposited on the topsurface of array interconnect layer 306 by one or more thin filmdeposition processes including, but not limited to, CVD, PVD, ALD, orany combination thereof. As illustrated in FIG. 3C, bonding contacts 310are formed in dielectric 308 to form a bonding layer 312 above arrayinterconnect layer 306 and memory array device layer 304. Bondingcontact 310 can be formed in multiple processes depending on thespecific indiffusible conductive material forming bonding contact 310.In one example, bonding contact 310 can include a barrier/adhesion layerand a conductor layer made of Co, Ta, W, Ti, or Ni depositedsubsequently in this order by one or more thin film deposition processesincluding, but not limited to, CVD, PVD, ALD, electrochemicaldepositions, or any combination thereof. Fabrication processes to formbonding contact 310 can also include photolithography, CMP, wet/dryetch, or any other suitable processes, to pattern and etch an opening(e.g., a via hole and/or a trench) in which the barrier/adhesion layerand conductor layer can be deposited. In another example, bondingcontact 310 made of CoSi, TaSi, WSi, TiSi, or NiSi can be formed bydepositing silicon and the respective metal using one or more thin filmdeposition processes including, but not limited to, CVD, PVD, ALD,electrochemical depositions, or any combination thereof, followed by ananneal (sintering) process resulting in the formation of correspondingmetal-Si alloy (metal silicide). In still another example, bondingcontact 310 made of CoN, TaN, WN, TiN, or NiN can be formed bydepositing the corresponding nitride compound using one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,electrochemical depositions, or any combination thereof. In someembodiments, bonding contact 310 made of CoN, TaN, WN, TiN, or NiN canbe formed by first depositing the corresponding metal, following bynitrogen implantation.

As illustrated in FIG. 3C, the top surface of bonding layer 312 isflattened for future bonding process. To ensure reliable bonding, insome embodiments, the step height between dielectric 308 and bondingcontact 310 is between about −20 nm and about 20 nm, such as between −20nm and 20 nm. Depending on the specific indiffusible conductive materialforming bonding contact 310, bonding layer 312 can be flattened by anysuitable processes, such as CMP or etching. In one example, bondingcontact 310 made of Co, Ta, W, Ti, or Ni can be flattened by a metal CMPprocess with slurry suitable for polishing metals. In another example,bonding contact 310 made of CoSi, TaSi, WSi, TiSi, or NiSi can beflattened by wet etching and/or drying etching. In still anotherexample, bonding contact 310 made of CoN, TaN, WN, TiN, or NiN can beflattened by wet etching and/or drying etching.

Method 600 proceeds to operation 608, as illustrated in FIG. 6, in whicha second device layer is formed above a second substrate. The secondsubstrate can be a silicon substrate. As illustrated in FIG. 4A, adevice layer 404 is formed on a silicon substrate 402. Device layer 404can be a peripheral device layer including a plurality of transistors(not shown) formed on silicon substrate 402 by a plurality of processesincluding, but not limited to, photolithography, dry/wet etch, thin filmdeposition, thermal growth, implantation, CMP, and any other suitableprocesses.

Method 600 proceeds to operation 610, as illustrated in FIG. 6, in whicha second interconnect layer is formed above the second device layer. Asillustrated in FIG. 4A, a peripheral interconnect layer 406 can beformed above peripheral device layer 404. Peripheral interconnect layer406 can include interconnects (not shown), including interconnect linesand via contacts in a plurality of ILD layers, to make electricalconnections with peripheral device layer 404. In some embodiments,peripheral interconnect layer 406 includes multiple ILD layers andinterconnects therein formed by multiple processes. For example, theinterconnects can include conductive materials deposited by one or morethin film deposition processes including, but not limited to, CVD, PVD,ALD, electrochemical depositions, or any combination thereof. The ILDlayers can include dielectric materials deposited by one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,or any combination thereof.

Method 600 proceeds to operation 612, as illustrated in FIG. 6, in whicha second bonding layer including a second bonding contact is formedabove the second interconnect layer. A second dielectric can be formedin the second bonding layer as well. The second bonding contact is madeof a second indiffusible conductive material, according to someembodiments. In some embodiments, the second indiffusible conductivematerial is not Cu. The second indiffusible conductive material can beselected from the group consisting of Co, Ta, W, Ti, Ni, CoN, TaN, WN,TiN, NiN, CoSi, TaSi, WSi, TiSi, and NiSi. The second bonding layer canbe flattened by CMP or etching, such that a second step height betweenthe second dielectric and the second bonding contact is between about−20 nm and about 20 nm. In some embodiments, the second interconnect ismade of a conductive material (e.g., Cu or Al) other than the secondindiffusible conductive material. In some embodiments, the firstindiffusible conductive material is the same as the second indiffusibleconductive material. In some embodiments, the first indiffusibleconductive material is different from the second indiffusible conductivematerial.

As illustrated in FIG. 4B, a dielectric 408 is deposited on the topsurface of peripheral interconnect layer 406 by one or more thin filmdeposition processes including, but not limited to, CVD, PVD, ALD, orany combination thereof. As illustrated in FIG. 4C, bonding contacts 410are formed in dielectric 408 to form a bonding layer 412 aboveperipheral interconnect layer 406 and peripheral device layer 404.Bonding contact 410 can be formed in multiple processes depending on thespecific indiffusible conductive material forming bonding contact 410.In one example, bonding contact 410 can include a barrier/adhesion layerand a conductor layer made of Co, Ta, W, Ti, or Ni depositedsubsequently in this order by one or more thin film deposition processesincluding, but not limited to, CVD, PVD, ALD, electrochemicaldepositions, or any combination thereof. Fabrication processes to formbonding contact 410 can also include photolithography, CMP, wet/dryetch, or any other suitable processes, to pattern and etch an opening(e.g., a via hole and/or a trench) in which the barrier/adhesion layerand conductor layer can be deposited. In another example, bondingcontact 410 made of CoSi, TaSi, WSi, TiSi, or NiSi can be formed bydepositing silicon and the respective metal using one or more thin filmdeposition processes including, but not limited to, CVD, PVD, ALD,electrochemical depositions, or any combination thereof, followed by ananneal (sintering) process resulting in the formation of correspondingmetal-Si alloy (metal silicide). In still another example, bondingcontact 410 made of CoN, TaN, WN, TiN, or NiN can be formed bydepositing the corresponding nitride compound using one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,electrochemical depositions, or any combination thereof. In someembodiments, bonding contact 410 made of CoN, TaN, WN, TiN, or NiN canbe formed by first depositing the corresponding metal, following bynitrogen implantation.

As illustrated in FIG. 4C, the top surface of bonding layer 412 isflattened for future bonding process. To ensure reliable bonding, insome embodiments, the step height between dielectric 408 and bondingcontact 410 is between about −20 nm and about 20 nm, such as between −20nm and 20 nm. Depending on the specific indiffusible conductive materialforming bonding contact 410, bonding layer 412 can be flattened by anysuitable processes, such as CMP or etching. In one example, bondingcontact 410 made of Co, Ta, W, Ti, or Ni can be flattened by a metal CMPprocess with slurry suitable for polishing metals. In another example,bonding contact 410 made of CoSi, TaSi, WSi, TiSi, or NiSi can beflattened by wet etching and/or drying etching. In still anotherexample, bonding contact 410 made of CoN, TaN, WN, TiN, or NiN can beflattened by wet etching and/or drying etching.

Method 600 proceeds to operation 614, as illustrated in FIG. 6, in whichthe first substrate and the second substrate are bonded in aface-to-face manner, such that the first bonding contact is in contactwith the second bonding contact at a bonding interface. The firstdielectric can be in contact with the second dielectric as well afterthe bonding. The bonding can be hybrid bonding.

As illustrated in FIG. 5A, silicon substrate 302 and memory array devicelayer 304 formed thereon are flipped upside down. Bonding layer 312facing down is to be bonded with bonding layer 412 facing up, i.e., in aface-to-face manner. In some embodiments, bonding contacts 410 arealigned with bonding contacts 310 prior to hybrid bonding, so thatbonding contacts 410 are in contact with bonding contacts 310 after thehybrid bonding, according to some embodiments. In some embodiments, atreatment process, e.g., a plasma treatment, a wet treatment, and/or athermal treatment, is applied to the bonding surfaces prior to thehybrid bonding. As a result of the hybrid bonding, bonding contacts 410can be inter-mixed with bonding contacts 310, and dielectric 408 can becovalent-bonded with dielectric 308, thereby forming a bonding interface502 between bonding layer 412 and bonding layer 312, as shown in FIG.5B. Silicon substrate 302 is thinned or fully removed after the bonding,according to some embodiments.

It is understood that although memory array device layer 304 is flippedupside down and is above peripheral device layer 404 in the resultingsemiconductor device as shown in FIG. 5B, in some embodiments,peripheral device layer 404 is flipped upside down and is above memoryarray device layer 304 in the resulting semiconductor device. It isfurther understood that although device layer 304 is illustrated as amemory array device layer and device layer 404 is illustrated as aperipheral device layer, the examples are for illustrative purposes onlyand do not limit the embodiments of present disclosure. In one example,device layer 304 can be a peripheral device layer, and device layer 404can be a memory array device layer. In another example, device layers304 and 404 can be both peripheral device layers. In still anotherexample, device layers 304 and 404 can be both memory array devicelayers.

According to one aspect of the present disclosure, a semiconductordevice includes a first semiconductor structure, a second semiconductorstructure, and a bonding interface between the first semiconductorstructure and the second semiconductor structure. The firstsemiconductor structure includes a substrate, a first device layerdisposed on the substrate, and a first bonding layer disposed above thefirst device layer and including a first bonding contact. The secondsemiconductor structure includes a second device layer and a secondbonding layer disposed below the second device layer and including asecond bonding contact. The first bonding contact is in contact with thesecond bonding contact at the bonding interface. At least one of thefirst bonding contact or the second bonding contact is made of anindiffusible conductive material.

In some embodiments, the indiffusible conductive material is not Cu. Insome embodiments, the indiffusible conductive material is selected fromthe group consisting of Co, Ta, W, Ti, Ni, CoN, TaN, WN, TiN, NiN, CoSi,TaSi, WSi, TiSi, and NiSi.

In some embodiments, the first bonding contact is made of a firstindiffusible conductive material, and the second bonding contact is madeof a second indiffusible conductive material. In some embodiments, thefirst indiffusible conductive material is the same as the secondindiffusible conductive material. In some embodiments, the firstindiffusible conductive material is different from the secondindiffusible conductive material.

In some embodiments, the first bonding layer further includes a firstdielectric, and the second bonding layer further includes a seconddielectric in contact with the first dielectric at the bondinginterface. In some embodiments, a first step height between the firstdielectric and the first bonding contact is between about −20 nm andabout 20 nm, and a second step height between the second dielectric andthe second bonding contact is between about −20 nm and about 20 nm. Eachof the first dielectric and the second dielectric is made of siliconoxide, according to some embodiments.

In some embodiments, the first semiconductor structure further includesa first interconnect layer including a first interconnect between thefirst device layer and the first bonding layer, and the secondsemiconductor structure further includes a second interconnect layerincluding a second interconnect between the second device layer and thesecond bonding layer. Each of the first interconnect and the secondinterconnect is made of a conductive material other than theindiffusible conductive material, according to some embodiments.

In some embodiments, one of the first device layer and the second devicelayer includes a NAND memory string, and another one of the first devicelayer and the second device layer includes a peripheral device.

According to another aspect of the present disclosure, a bondedstructure includes a first bonding layer including a first bondingcontact and a first dielectric, a second bonding layer including asecond bonding contact and a second dielectric, and a bonding interfacebetween the first bonding layer and the second bonding layer. The firstbonding contact is in contact with the second bonding contact at thebonding interface, and the first dielectric is in contact with thesecond dielectric at the bonding interface. Each of the first bondingcontact and the second bonding contact is made of a same indiffusibleconductive material other than Cu.

In some embodiments, the indiffusible conductive material is selectedfrom the group consisting of Co, Ta, W, Ti, Ni, CoN, TaN, WN, TiN, NiN,CoSi, TaSi, WSi, TiSi, and NiSi.

In some embodiments, a first step height between the first dielectricand the first bonding contact is between about −20 nm and about 20 nm,and a second step height between the second dielectric and the secondbonding contact is between about −20 nm and about 20 nm. Each of thefirst dielectric and the second dielectric is made of silicon oxide,according to some embodiments.

According to still another aspect of the present disclosure, a methodfor forming a semiconductor device is disclosed. A first device layer isformed above a first substrate. A first bonding layer including a firstbonding contact is formed above the first device layer. The firstbonding contact is made of a first indiffusible conductive material. Asecond device layer is formed above a second substrate. A second bondinglayer including a second bonding contact is formed above the seconddevice layer. The first substrate and the second substrate are bonded ina face-to-face manner, such that the first bonding contact is in contactwith the second bonding contact at a bonding interface.

In some embodiments, the second bonding contact is made of a secondindiffusible conductive material.

In some embodiments, each of the first indiffusible conductive materialand the second indiffusible conductive material is not Cu. In someembodiments, each of the first indiffusible conductive material and thesecond indiffusible conductive material is selected from the groupconsisting of Co, Ta, W, Ti, Ni, CoN, TaN, WN, TiN, NiN, CoSi, TaSi,WSi, TiSi, and NiSi.

In some embodiments, the first indiffusible conductive material is thesame as the second indiffusible conductive material. In someembodiments, the first indiffusible conductive material is differentfrom the second indiffusible conductive material.

In some embodiments, to form the first bonding layer, a first dielectricis formed in the first bonding layer; to form the second bonding layer,a second dielectric is formed in the second bonding layer; and the firstdielectric is in contact with the second dielectric at the bondinginterface after the bonding.

In some embodiments, to form the first bonding layer, the first bondinglayer is flattened, such that a first step height between the firstdielectric and the first bonding contact is between about −20 nm andabout 20 nm; and to form the second bonding layer, the second bondinglayer is flattened, such that a second step height between the seconddielectric and the second bonding contact is between about −20 nm andabout 20 nm. The flattening can include CMP or etching.

In some embodiments, each of the first dielectric and the seconddielectric is made of silicon oxide.

In some embodiments, a first interconnect layer including a firstinterconnect is formed between the first device layer and the firstbonding layer, and a second interconnect layer including a secondinterconnect is formed between the second device layer and the secondbonding layer. Each of the first interconnect and the secondinterconnect is made of a conductive material other than the firstindiffusible conductive material or the second indiffusible conductivematerial, according to some embodiments.

In some embodiments, to form one of the first device layer and thesecond device layer, a NAND memory string is formed; and to form anotherone of the first device layer and the second device layer, a peripheraldevice is formed.

In some embodiments, the bonding includes hybrid bonding.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A semiconductor device, comprising: a firstsemiconductor structure comprising a substrate, a first device layerdisposed above the substrate, and a first bonding layer disposed abovethe first device layer and comprising a first bonding contact; a secondsemiconductor structure comprising a second device layer, and a secondbonding layer disposed below the second interconnect layer andcomprising a second bonding contact; and a bonding interface between thefirst semiconductor structure and the second semiconductor structure,wherein the first bonding contact is in contact with the second bondingcontact at the bonding interface; wherein at least one of the firstbonding contact or the second bonding contact is made of an indiffusibleconductive material; wherein the indiffusible conductive material isselected from a group consisting of Ta, Ti, Ni, CoN, TaN, WN, TiN, NiN,CoSi, TaSi, WSi, TiSi, and NiSi, wherein the first bonding layer furthercomprises a first dielectric, and the second bonding layer furthercomprises a second dielectric in contact with the first dielectric atthe bonding interface, and wherein a first step height between the firstdielectric and the first bonding contact is between about −20 nm andabout 20 nm, and a second step height between the second dielectric andthe second bonding contact is between about −20 nm and about 20 nm. 2.The semiconductor device of claim 1, wherein the first bonding contactis made of a first indiffusible conductive material, and the secondbonding contact is made of a second indiffusible conductive material. 3.The semiconductor device of claim 2, wherein the first indiffusibleconductive material is the same as the second indiffusible conductivematerial.
 4. The semiconductor device of claim 2, wherein the firstindiffusible conductive material is different from the secondindiffusible conductive material.
 5. The semiconductor device of claim1, wherein each of the first dielectric and the second dielectric ismade of silicon oxide.
 6. The semiconductor device of claim 1, wherein:the first semiconductor structure further comprises a first interconnectlayer comprising a first interconnect between the first device layer andthe first bonding layer; the second semiconductor structure furthercomprises a second interconnect layer comprising a second interconnectbetween the second device layer and the second bonding layer; andwherein each of the first interconnect and the second interconnect ismade of a conductive material other than the indiffusible conductivematerial.
 7. The semiconductor device of claim 1, wherein one of thefirst device layer and the second device layer comprises a NAND memorystring, and another one of the first device layer and the second devicelayer comprises a peripheral device.
 8. A bonded structure, comprising:a first bonding layer comprising a first bonding contact and a firstdielectric; a second bonding layer comprising a second bonding contactand a second dielectric; and a bonding interface between the firstbonding layer and the second bonding layer, wherein the first bondingcontact is in contact with the second bonding contact at the bondinginterface, and the first dielectric is in contact with the seconddielectric at the bonding interface; wherein at least one of the firstbonding contact or the second bonding contact is made of an indiffusibleconductive material other than Cu; and wherein the indiffusibleconductive material is selected from a group consisting of Ta, Ti, Ni,TaN, TiN, and NiN.
 9. The bonded structure of claim 8, wherein the firstbonding contact is made of a first indiffusible conductive material, andthe second bonding contact is made of a second indiffusible conductivematerial.
 10. The bonded structure of claim 9, wherein the firstindiffusible conductive material is the same as the second indiffusibleconductive material.
 11. The bonded structure of claim 9, wherein thefirst indiffusible conductive material is different from the secondindiffusible conductive material.
 12. The bonded structure of claim 8,wherein each of the first dielectric and the second dielectric is madeof silicon oxide.
 13. A semiconductor device, comprising: a firstsemiconductor structure comprising a substrate, a first device layerdisposed above the substrate, a first interconnect disposed above thefirst device layer, and a first bonding layer disposed above the firstinterconnect and comprising a first bonding contact; a secondsemiconductor structure comprising a second device layer, a secondinterconnect disposed below the second device layer, and a secondbonding layer disposed below the second interconnect and comprising asecond bonding contact; and a bonding interface between the firstsemiconductor structure and the second semiconductor structure, whereinthe first bonding contact is in contact with the second bonding contactat the bonding interface; wherein at least one of the first interconnectand the second interconnect comprise copper; wherein at least one of thefirst bonding contact or the second bonding contact is made of anindiffusible conductive material; wherein the indiffusible conductivematerial is selected from a group consisting of Ta, Ti, Ni, CoN, TaN,WN, TiN, NiN, CoSi, TaSi, WSi, TiSi, and NiSi, wherein the first bondinglayer further comprises a first dielectric, and the second bonding layerfurther comprises a second dielectric in contact with the firstdielectric at the bonding interface, and wherein a first step heightbetween the first dielectric and the first bonding contact is betweenabout −20 nm and about 20 nm, and a second step height between thesecond dielectric and the second bonding contact is between about −20 nmand about 20 nm.
 14. The semiconductor device of claim 13, wherein theconductive material of the first interconnect and the secondinterconnect is copper.
 15. The semiconductor device of claim 1, whereinthe first bonding contact is made of the indiffusible conductivematerial, and the second bonding contact is made of copper.
 16. Thesemiconductor device of claim 13, wherein the first bonding contact ismade of the indiffusible conductive material, and the second bondingcontact is made of copper.